1. Field of the Invention
The present invention relates to a system for optically interrogating non-homogeneous samples of liquid by scanning the samples with a beam of light to locate regions of interest, and for withdrawing liquid from the regions of interest. Features of the present invention are especially useful in interrogating centrifuged samples of liquids that have distinct layers of components at different height levels within test tubes, wherein it is desired to remove sample portions that comprise one or more of the layers.
2. Prior Art
Inspection and detection systems of many forms have been proposed that utilize visible and/or invisible electromagnetic radiation as a projected medium for interrogating objects including samples of liquid, with transmission, reflection, refraction or other characteristics being detected to determine information about the interrogated samples. It has been proposed, for example, to scan a solid object with a beam of laser light, and to detect the intensity of the reflected light, with sensed differences in reflected light intensity being indicative of the locations of physical features of the object that are known to exist within a designated area of investigation.
Automated systems of various types have been proposed for effecting sequential movements of container carried samples of liquid to and from test stations for examination, treatment, and/or withdrawal of portions of the samples from their containers. For example, apparatus for effecting automated testing of samples of body fluids such as blood and urine are known, with the apparatus typically having capabilities to extract sample portions and to subject the extracted liquids to various types of tests and measurements. However, these automated systems are intended for use with samples that are substantially homogeneous in character, not for use with non-homogeneous samples such as centrifuged samples of liquid that have layers that differ in consistency.
Despite a plethora of proposals that have been made in efforts to provide a variety of automated inspection, detection, and sampling systems, a technique that continues to be used as a mainstay in laboratories where thin layers of centrifuged samples of liquid must be withdrawn, is manual precision pipetting. This technique includes the steps of inserting pipettes into container-carried samples of centrifuged liquid, with the insertion of the pipettes being guided by eye and hand coordination, and with the precision of the withdrawal of selected sample portions being determined by the, skill, care and luck of the laboratory technician who performs these manual tasks. In situations where centrifuged samples have extremely thin layers of liquid that are to be withdrawn, with these very thin layers of interest typically being in the range of about 10 to 50 microns in thickness, the use of manual precision pipetting techniques by even the most skilled and experienced technicians achieve results that vary widely from one pipetting operation to the next. The results vary both in the percentages of the desired components that escape extraction, and in the percentages of unwanted liquid components are found to be included in the liquid that has been extracted. A nearly perfect extraction (i.e., an extraction that succeeds in withdrawing substantially all of the desired components with substantially no accompanying withdrawal of unwanted components) is rarely achieved.
Thus, a long-standing need has remained unfulfilled for a method and apparatus that will enable selected portions of liquid samples to be located and extracted accurately and effectively, sample after sample. The need has been especially prevalent where centrifuged samples of liquid contain extremely thin layers of liquid at various height levels that must be located and extracted with extreme accuracy, with exacting degrees of control being required both in positioning pipettes that are used to withdraw liquid from the thin layers of interest, and in conducting thorough extractions of components that comprise the layers of interest but without causing the accompanying extraction of undesired components.